This invention relates to side bearings of the type for use in railroad vehicles. Such a side bearing ordinarily is a resilient, vibration-damping, energy-absorbing device positioned between a railroad car body and a truck bolster and adapted to be compressed under static preload forces and to absorb forces encountered as the car body swings in order to reduce the oscillating or "rolling" action of the car body with respect to its longitudinal center line and the "hunting" action of the wheel truck assembly, that is, the torsional oscillation of the wheel truck assembly about the point of attachment to the car body, thereby permitting higher operating speeds without derailment.
Side bearings have been known for many years employing rollers movably mounted in a frame supported on a truck bolster which could be contacted by the car body. Also, preloaded side bearings are known utilizing spring-loaded cam systems resulting in a complicated construction. Insofar as solving the problem of "rolling" oscillations resulting in derailments, it has been known to utilize snubber members used in conjunction with the spring groups between the truck bolster and the side frame of the truck. None of the foregoing, as well as other variations thereof, has been found to provide an inexpensive structure for the reduction of the "rolling" oscillations which cause the car bodies to sway from side to side, thereby creating the problem known in the railroad industry as "rock and roll".
U.S. Pat. Nos. 3,556,503 and 3,628,464 suggest using a resilient side bearing in the approximate shape of a frustum of a cone with a top surface having a sloping outer portion and made from a hard elastomeric material with a base, positioned between the railroad car body and a truck bolster, and adapted to be compressed under both static preloading forces and the alternating cycling loading forces generated by the "rolling" and "hunting" oscillations of the car under dynamic conditions. This device functions by absorbing the kinetic energy of the "rolling" and "hunting" and converting it into heat energy. I have found that under simulated, in-service conditions where the side bearing is made from a hard polyurethane elastomer, and the top surface has either a flat, medial portion with a sloping outer top surface portion, as described in U.S. Pat. No. 3,556,503, or a cylindrical axial bore with a metal insert, as described in U.S. Pat. No. 3,628,464, the distribution of the internal strain, is inefficient and causes undesirably rapid build-up of internal temperatures to between 250.degree.F. and 400.degree.F. and premature failure of the side bearing.